Starting in 1912 he actively joined the labour movement, participating in many work-related actions by Iași typographers and textile workers.

Between 1923 and 1931, he served as secretary of the local workers' commission in Iași, affiliated with the General Council of Unitary Romanian Trade Unions.

He had an important role in the demonstrations at the Iaşi People's House (set up between 1918 and 1921), in printing the newspaper Moldova Roşie ("Red Moldavia") in the nearby village of Vlădiceni, in obtaining important documents needed for underground work, as well as in the activity of other workers' and socialist organisations in Iași.

After a coup overthrew Ion Antonescu's régime on August 23, 1944 (see Romania during World War II), he was given sensitive party and state posts.

When the Romanian People's Republic was proclaimed on December 30, 1947, Niculi was elected member (vice president) of the Presidium of the Romanian People's Republic, serving from that date until April 13, 1948, alongside Constantin Ion Parhon, Mihail Sadoveanu, Ștefan Voitec, and Gheorghe Stere [ro].